Effect of Mn Doping on the Structural and Ferroelectric properties of SrBi₂Ta₂O₉

Abstract

SrBi₂Ta₂O₉ (SBT) samples have been prepared by sol-gel technique with varying amount of excess Bi added to the starting composition. The excess Bi profoundly affects the dielectric and ferroelectric properties. The dielectric constant (ε) and remnant polarization increases from 80 and 1.4 μ C/cm² for SBT with 1 mole % of excess Bi to 120 and 6.5 μ C/cm² for SBT with 20 mole % of excess Bi. The Raman spectra, scanning electron microscopy images and the x-ray diffraction analysis show an improvement in structural quality of the samples with addition of excess Bi to the starting composition. The effect of Mn doping has also been studied by preparing SrBi₂Ta_2-x Mn_x O₉ (SBT-Mn) with x = 0–0.1. In the case of SBT-Mn samples, the XRD spectra revealed an unknown phase when x > 0.025. However, Raman spectra reveal the retention of Bi layer structure for all Mn compositions, with possibly small distortions. With Mn addition, ε increased to ∼ 140 for x < 0.005, but decreased to ≤ 120 when x > 0.015. The value of ε is independent of frequency from 60 to 85 kHz for all compositions of Mn. The effect of Mn addition resulted in a strong decrease in the area of the hysteresis loops.